Confounding Ferns

This is a new file, opened on February 21, 2015, for “A Tale of Two Confounding Ferns”, an article for the summer 2015 issue of Kaatskill Life.

A TALE OF TWO CONFOUNDING FERNSby Michael Kudish

I had been forcing my way off-trail through seas of ferns often so dense that I could not see a downed log or small boulder a foot in front of me. I pushed my sample plot measuring stick ahead so that it would crash into an obstacle before my knees did. Soon I learned that these ferns were so abundant that they were controlling the site and prohibiting trees and other plants from growing.

This was when I was a graduate student, preparing a dissertation on the history of Catskills forests. The seas of ferns were especially – but not solely - at elevations above 2800 or 2900 feet.

The confounding ferns were the woodferns. The reference books at that time considered the plants as two varieties of the same species, the spinulose woodfern, Dryopteris spinulosa. The two varieties were the evergreen woodfern and the mountain woodfern. I suspected that there might be two species involved here instead of one. For over forty years the puzzle nagged and nagged.

Finally, on October 31, 2014, a cool clear day on Balsam Lake Mountain, I had a revelation. It was a Friday and I had the whole mountain to myself – not one other hiker seen all day. I could concentrate fully, moving ever so slowly up the mountain observing, measuring, and writing. By about noon, at about elevation 3300 feet, the 45-year old puzzle was finally solved!

Most botanical authors base their classifications on morphological features (what the plants look like) and more recently on genetic features. My classification was based more on the ecology (how the ferns relate to the site that they grow on) and their behavior.

There are indeed two species: (1) The evergreen woodfern, Dryopteris intermedia, and --- (2) The mountain woodfern, Dryopteris campyloptera.

EVERGREEN VS. DECIDUOUS

Both species in summer look very much alike, the mountain woodfern being a little larger of the two although there is considerable overlap in size. From dozens of my measurements, the fronds (i.e. leaves) of evergreen woodfern range from 10 to 36 inches long from ground level to the tip. The median leaf length is 20 inches. Mountain woodfern ranges in height from 15 to 46 inches, with a median at about 27.5 inches.

It is in the fall that one really begins to see the difference between the two. The evergreen woodfern is just that – it remains evergreen. The leaves overwinter almost unchanged under the snow. In spring, after snow melt, the leaves are lying almost on the ground, but still photosynthesizing until the new year’s leaves emerge – typically in late May or June. Therefore, there are green leaves on the plant all year long.

Mountain woodfern is different. It is deciduous. It is usually in September when the leaves begin to turn purple and/or ultimately brown. They dry out, wilt, become crisp, and droop. When trying to lift the leaves in late October in order to measure them, they snap and break with the gentlest touch. After snowmelt in spring, they form a brown, almost unrecognizable mat on the ground floor. The new leaves in the spring begin to appear well before those of the evergreen woodfern. And why not? The evergreen woodfern still has its previous year’s leaves to work with while the mountain woodfern does not.

ECOLOGY: SHADE TOLERANCE AND ELEVATION

There is quite a difference between these two species in their ability to tolerate shade. Evergreen woodfern is one of the most shade-tolerant ferns, if not THE most shade-tolerant fern in the Catskills. It will grow under northern hardwoods (sugar maple, beech, yellow birch, black cherry, red maple), and under conifers (eastern hemlock, red spruce, balsam fir) in all but the very darkest places. Under stands of dense hemlock, it may be the only ground cover plant present (except for some mosses) and is dwarfed in such shade; the leaves are only from 10 to 16 inches long. In partial shade under northern hardwoods, the leaves can become much larger, from 20 to 36 inches long. Its elevation range is very wide, from below 1000 feet to at least 3700 feet.

Mountain woodfern provides quite a contrast. It is only moderately shade-tolerant. It will not grow with the evergreen woodfern under dense hemlock, fir, spruce, or beech. Rather, it thrives in places where there is sun for a portion of the day. Therefore, it is most abundant in forest stands that are partly open – where there are scattered trees and/or small islands (i.e., groves) of trees surrounded by seas of open, sunny fern glades (see the summer 2011 issue of Kaatskill Life, pages 74 to 80, for an article on fern glades).

These semi-open forest stands exist because of chronic wind, snow, and ice disturbance, and/or where the soils are so thin over bedrock ledges that a continuous forest canopy cannot be supported. Such semi-open stands are found typically at the higher elevations – usually above 2800 or 2900 feet all the way up to over 4000 feet.

Here, in this semi-open forest, is the best place to observe both ferns, as I did on Balsam Lake Mountain.

Look in the shade under groves of trees. There you will find the evergeen woodfern. Now look at the middle of the glade of ferns; here is the shade-intolerant, sun-loving hay-scented fern, Dennstaedtia punctilobula. The hay-scented fern is so distinct from all other ferns that it never confounded me with its identification.

Finally, look around the edges of the groves of trees, between the evergreen woodfern and the hay-scented. Here is where you will find the somewhat shade-tolerant mountain woodfern.

WHY CONFOUNDED?

Why had I found the two ferns so confounding for so many decades? One reason I stated above: the botanical manuals at that time considered the two ferns only varieties of the same species. My observations were telling me that something was wrong with this classification. How could some plants be evergreen and others deciduous within the same species? It seemed impossible.

Another reason is that the two ferns look very much alike, especially in the summer months when they are all green, and they overlap so in size.

The third reason I just realized last October on Balsam Lake Mountain. The mountain woodfern can be very variable in the time of the year when its leaves begin to senesce – some plants as early as August and others not until October. They also turn different colors – some more purple, some more brown, and some with persistent green blotches and splotches in an otherwise purple or brown background.

GENETICS

The more recent fern books do consider the woodferns as two distinct species – finally. This has been proved genetically, but there is no room here to go into a detailed explanation. One might wonder whether the two ferns species cross. Very unlikely. Hybridization, and resulting plants with in-between features, may be possible for only a single generation, but the offspring are sterile.

FOREST HISTORY

The title of this series of articles in Kaatskill Life is “The Kaatskill Forest Historian”. Therefore, I should add some forest history regarding these ferns, but unfortunately I have little to report on how and when they migrated post-glacially into the Catskills. I have not yet found fossil woodfern parts in the peat bog samples. This may be because mountain woodfern does not usually grow in bogs. Evergreen woodfern is not abundant in them, and may rot rapidly. Because of their northern distribution today well into Canada, and because of what company they keep (i.e. the other plants they associate with), I suspect that the two species have been here for a very long time - perhaps between 10000 and 14000 years.